Line pickup is a type of noise that can be especially troubling when the signals which are affected by the pickup are relatively small. For example, signals such as ECG (electrocardiogram) signals may typically be relatively small compared to the line noise picked up by leads acquiring the signals. Methods for reducing the effects of this type of noise are known in the art.
U.S. Pat. No. 6,041,250, to dePinto, whose disclosure is incorporated herein by reference, describes an adaptive line noise detection and cancellation system. The system is stated to have, inter alia, a baseline wander filter, high and low pass filters, and an adaptive line noise canceler. The system is also stated to be able to identify and remove contamination from an ECG signal.
U.S. Pat. No. 8,597,196, to Kishi et al., whose disclosure is incorporated herein by reference, describes a cardiac signal processing apparatus which is stated to include a unit for acquiring, from a heartbeat sensor, cardiac signals relating to heartbeats of a subject. The apparatus is also stated to have a low-pass filter for allowing passage of those cardiac signals having a first predetermined frequency or lower, among the cardiac signals, and a higher harmonic noise acquisition unit for acquiring harmonic signals of low-frequency noise by performing high frequency extrapolation on the signals output from the low-pass filter.
U.S. Pat. No. 8,134,255, to Hatanaka et al., whose disclosure is incorporated herein by reference, describes a noise cancellation circuit. The circuit is stated to have a cancellation signal generation section that generates a cancellation signal which cancels an alternating-current component of a power supply terminal voltage of a digital signal processing circuit section. There is also a synthesis section which synthesizes the generated cancellation signal and a power supply voltage of an analog signal processing circuit section to cancel noise superimposed on the power supply voltage.
An article titled “FPGA-Based Implementation of an Adaptive Canceller for 50/60-Hz Interference in Electrocardiography,” published in IEEE Transactions on Instrumentation and Measurement, Vol. 56, No. 6, December 2007, to Ramos et al., is incorporated herein by reference. The article describes an adaptive canceller which uses an adaptive filter.
An article titled “Noise removal from ECG Using Modified CSLMS algorithm,” published in International Journal of Electronics, Communication & Instrumentation Engineering Research and Development Vol. 4, Issue 3, June 2014, to Rehman, et al, is incorporated herein by reference. The article refers to an adaptive filter that “mainly” minimizes the mean squared error between a primary input and a reference input.
Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that, to the extent that any terms are defined in these incorporated documents in a manner that conflicts with definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered.